Measurement of position is required in many applications. The most common measurement sensor is probably a mechanical potentiometer whereby a position is functionally related to the position of a sliding wiper, movable over a resistive track. The wiper is moved by an actuator whose position is to be measured. Some applications require a large number of sequential measurements, resulting in destructive wear of mechanical potentiometer components.
Accordingly, the inventor believes that it's desirable to have an electronic, non-contact, angle or position sensor, thereby eliminating any mechanical wear between a sensor contact wiper and a resistive track.
Many inventions teach electronic means for measuring position, based upon a broad array of actuators and sensors functionally dependent on physical parameters that change with position. Specific examples of physical parameters and their functional relationships for measurement of position are capacitance, optical, magnetic, electromagnetic, inductive, strain and combinations of these parameters. U.S. Pat. No. 5,773,820 references optical, U.S. Pat. Nos. 6,756,779 and 6,483,295 reference inductive, U.S. Pat. Nos. 6,362,719 and 6,486,767 reference strain gages, U.S. Pat. Nos. 6,809,512, 6,806,701, 6,498,480, 6,779,389, 6,717,399, and 6,798,195 reference magnetic, U.S. Pat. No. 6,393,912 references electromagnetic and U.S. Pat. Nos. 5,736,865 and 6,118,283 reference capacitive.
Published Patent Applications US 2004/0003660, 2004/0168467, 2005/0217366, and 2005/0247124 teach an encapsulated, linear, magnetic sensor, sensing a varying magnetic field from an annular ring magnet diametrically magnetized that is rotated by an actuator. The linear output voltage can be converted to a pulse-width-modulated (PWM) signal for transmission.
A generally common technical thread running through these inventions is that a sensor puts out a signal that directly represents the measured parameter. The output signal may be linear or non-linear. If the signal is non-linear it may be processed to develop a linear result. If the signal is a simple change in voltage or resistance, a processing stage can convert the signal to another form for transmission, e.g. a voltage signal may be converted into PWM for transmission.
Another parameter measurement technique is a closed-loop electronic method, balancing or compensating a changing parameter value that can be sensed in a closed-, analog, or digital loop rather than with a direct sensor output signal of a parameter measurement. In this case a second, controlled signal is used to generate a variable value of the parameter being measured. A sensor is used to detect the difference or superimposed interaction between the parameter signal to be measured and a secondary, controlled parameter value signal. When the controlled value and the unknown value match, i.e. balance, the sensor puts out a signal disclosing the match that is not dependent on the matching values. The value of the control signal needed for the secondary parameter value to match the unknown parameter value determines the value of the unknown signal. This is sometimes called a null or balance measurement. The parameter may be any generated physical signal such as from force, position, angle or magnetic field. A simple balance scale is an example of a force balancing measurement. An unknown weight in one tray is balanced by varying a known weight in the other tray until the scale pointer is at zero. The unknown weight then matches the known weight. The scale pivot only has to be good at zero balance. Accuracy is determined mostly by accuracy of the known weights that are used to balance the scale. The scale pivot reads zero at balance regardless of the weight being measured.
Force balance methods of measurement are well known to those skilled-in-the-art. U.S. Pat. No. 6,618,325 describes a single-coil geophone that uses a force-balance. U.S. Pat. No. 6,496,348 teaches a force-balance feedback measurement with a capacitive sensor. Magnetic field cancellation or balance for measuring current is taught in U.S. Pat. No. 4,596,950. Null detection is used in U.S. Pat. No. 6,750,751 develop an integrated circuit signal isolator, including a feedback coil coupled to the output of the magnetic field sensor.
A major advantage of these signal balance methods is that the sensor does not have to develop a highly linear output or have a low temperature drift at all values of the measured parameter; many sensors have zero or very low temperature coefficients near zero signal field. Its sensor should be highly repeatable at the value of the trip or trigger point that is usually, but not necessarily, at zero force or field. It's also desirable for the sensor to be very sensitive to any change in the measured parameter. Finally, its necessary for the compensating or balancing signal to be accurately controllable in order to determine the balance, e.g. the accuracy of known weights used on a weight balance scale. Although force or field balancing has been used in many fields, the inventor believes that a direct application to position, or angular measurement in a pedal position or fuel level sender application is not known. No single, electronic, non-contact angular measurement sensor has proven to be completely satisfactory for all vehicular applications, such as fuel level senders, throttle position sensors, and pedal position sensors . Per-unit cost, even in large volume, is often too great and becomes the limiting factor for commercial success of an electronic angle or position sensor for vehicles. Accordingly, the inventor considers it desirable to have a non-contact or long-life sensor for measuring angle or position that is cost competitive with mechanical methods.